The present invention relates to a rotary fiberization process and apparatus and, in particular, to a rotary fiberization process and apparatus which utilizes a rotary fiberizer equipped with a burner/air ring assembly wherein pressurized air is used to cool an annular air cooled burner and then supplied to an air ring where it is discharged into the fiberization zone of the process at a high velocity.
The use of high velocity pressurized or compressed air to augment rotary glass fiberization processes is common in the glass fiber industry. The rotary fiberizer of these processes employ rotary fiberizing rotors and air rings. Molten glass is introduced into the rotating fiberizing rotors and fiberized by passing outward through orifices in the peripheral sidewalls of the fiberizing rotors. In the air rings, high pressure air is distributed by means of an annular manifold to narrow slots or small diameter orifices and discharged through those narrow slots or small diameter orifices into the fiberization zones of the processes adjacent the outer surfaces of the fiberizing rotor sidewalls. The constrictions caused by these narrow slots or small diameter orifices are such as to impart high velocities to the air, approaching or slightly exceeding sonic velocities, as the air exits the manifolds through the slots or orifices and enters the fiberization zones of the processes. The momentum of the high velocity air in the fiberization zones is transferred to the glass fiber primaries as the glass fiber primaries are spun from the rotating fiberizing rotors used in these processes. This momentum accelerates the glass fiber primaries to higher attenuation velocities and attenuates the glass fibers to finer diameter fibers.
However, the effects of air rings on these processes are not all positive. The high velocity air jets from the air rings aspirate or draw considerable amounts of ambient air into the fiberization zones of these processes and there are several drawbacks to this phenomenon. First, an undetermined portion of the momentum of the air jets is consumed during the process of accelerating the ambient air as it is pulled into the fiberization zones by the air jets. However, a second, and more important effect, is the cooling effect that occurs on the outer surfaces of the rotor sidewalls from the flow of cool air over or adjacent the outer surfaces of the sidewalls.
One potential source of cool air that can be drawn into the fiberization zones of these processes is from the glass entry ports of the rotary fiberizer which permit the molten glass to be introduced into the rotating fiberizing rotor. The relatively cool ambient air can be drawn into the rotary fiberizer through these glass entry ports and from these ports over the upper edges of the rotating fiberizing rotors into the fiberization zones. This source of relatively cool ambient air is normally minimized by the use of natural gas burners which discharge hot combustion gases into the rotating fiberizing rotors. These natural gas burners both help to maintain the molten glass within the fiberizing rotors at a desired operating temperature and, through the operation of these burners at an air/gas throughput high enough to produce a slight positive pressure inside and above the fiberizing rotor, these burners also function to prevent or greatly reduce the amount of cool ambient air entering the rotary fiberizer through the entry port.
Another source for relatively cool ambient air to enter the fiberization zones is more critical. Due to the high rotational speeds of the fiberizing rotors, which typically rotate at over two thousand revolutions per minute, the bottom surfaces of the fiberizing rotors function like a fan and accelerate air radially outward off the bottom surfaces of the rotors. Studies indicate that this ambient air is drawn around the lower peripheral edges of the fiberizing rotors and upward along the rotor sidewalls, generally in the form of recirculation eddies, by the aspirating effects of the air being discharged from the air ring. The flow of the ambient air upward along the rotor sidewalls excessively cools the lower portions of the rotor sidewalls and create turbulent regions adjacent the lower portions of the rotor sidewalls that preclude the use of the lower portions of the rotors for fiberization thereby reducing the potential production rates of the fiberizing rotors.
A solution commonly used by the industry to solve this more critical problem, involves the placement of auxiliary burners concentrically above the fiberization zones that discharge annular streams of hot combustion gases downward and between the outer peripheral surfaces of the rotor sidewalls and the air rings. The momentum of the hot combustion gases from these burners contribute some to the attenuation of the primary fibers. However, typically, the contribution of the momentum of the hot combustion gases to the attenuation of the primary fibers relative to the attenuation caused by the momentum of the high velocity air jets from the air rings is relatively minor. The primary function of the hot combustion gases from the burners is to provide a source of hot gases to the fiberization zones with velocity vectors directed into the fiberization zones to reduce or eliminate the amount of inspirated air. This permits the use of the entire rotor sidewalls for fiberization by keeping more uniform vertical temperature profiles across the rotor sidewalls and by reducing or eliminating the eddies mentioned above.
However, the burners currently used to provide the hot combustion gases for the fiberization zones are heavy, massive refractory lined burners. While the refractory lining materials enable these refractory lined burners to function at the elevated temperatures required, the refractory lining materials in these burners add significantly to both the weight and the size of these burners. For example, one of these refractory lined burners, used with a fiberizing rotor that is about twelve inches in diameter, can weigh about twelve hundred pounds and have an outside diameter that is about twice the diameter of the fiberizing rotor. Thus, although these burners are commonly used in rotary fiberizer having fiberizing rotors ranging from about eight to fifteen inches in diameter, the weight and size that would be required for such burners in rotary fiberizer using larger diameter rotary fiberizing rotors (e.g. fiberizing rotors ranging from about eighteen to thirty inches in diameter) has been prohibitive. As a result, although the use of larger diameter fiberizing rotors (fiberizing rotors greater than fifteen inches in diameter) has increased the production capacities of rotary fiberizer, the inability to supply the fiberization zones of these rotary fiberizer with hot combustion gases to prevent or greatly reduce the inspiration of ambient air into the fiberization zones has precluded the full attainment of the production increases which would otherwise have been obtained through the use of the larger diameter fiberizing rotors. Thus, there has been a need to provide a lighter weight burner of smaller dimensions for use in rotary fiberizer having fiberizing rotors greater than fifteen inches in diameter to increase the production capacities of such rotary fiberizer.
The rotary fiberizer and method of the present invention includes a rotating fiberizing rotor for forming fibers from a molten fiberizable material and a burner/air ring assembly. A molten fiberizable material (e.g. glass) is fed into the fiberizing rotor through a glass entry port. The centrifugal forces generated by the rotation of the fiberizing rotor then cause the molten fiberizable material in the fiberizing rotor to pass outward through a plurality of fiberizing holes in an annular peripheral sidewall of the fiberizing rotor to form primary fibers from the fiberizable material. The primary fibers exiting the fiberizing orifices are introduced directly into a fiberization zone which surrounds the fiberizing rotor. In the fiberization zone which is maintained at an elevated temperature by the hot combustion gases from the burner of the of burner/air ring assembly, the primary fibers are attenuated and formed into finer diameter fibers by the momentum of the high velocity air jets or streams discharged from the air ring of the burner/air ring assembly.
The burner/air ring assembly is concentrically mounted relative to the fiberizing rotor and includes an annular air cooled burner and an annular air ring. The annular air cooled burner has an annular discharge slot or series of slots for discharging hot combustion gases in a generally downward direction into the fiberization zone adjacent an outer surface of the peripheral wall of the fiberizing rotor to maintain the fiberization zone at the temperature required for the proper attenuation of the primary fibers. The annular air ring has an annular discharge slot, slots or orifices located radially outward from the outer surface of the peripheral wall of the fiberizing rotor for discharging high volumes of pressurized air in high velocity jets or streams (typically approaching or slightly exceeding sonic velocities) in a generally downward direction into the fiberization zone to attenuate the primary fibers. The annular combustion chamber of the burner is made of a high temperature resistant alloy and is provided with a cooling jacket for controlling the temperature of combustion chamber walls so that the combustion chamber of the burner does not have be lined with a refractory material. Pressurized air is introduced into the cooling jacket, circulated through the cooling jacket, and discharged from the cooling jacket into the annular air ring from which the pressurized air is discharged through the annular discharge slot, slots or orifices of the annular air ring into the heated fiberization zone to attenuate the primary fibers.
With the apparatus and method of the present invention, the need for a burner with a refractory lined combustion chamber is eliminated. The elimination of the need for a burner with a refractory lined combustion chamber greatly reduces both the weight and size of the burner used in the burner/air ring assembly of the present invention and permits the use of the burner/air ring assembly of the present invention in rotary fiberizer employing large diameter fiberizing rotors e.g. fiberizing rotors eighteen to thirty or more inches in diameter as well as in rotary fiberizer employing smaller diameter fiberizing rotors. Thus, the added production potential of larger diameter fiberizing rotors can now be more fully realized. In addition, by using the same pressurized air for the combustion chamber coolant in the burner and the high velocity air jets or streams of the air ring, the added operating costs that would have been incurred by using a second air supply to cool the burner is eliminated.
While air cooled burners exist which are cooled by the incoming combustion air that is burned in the combustion chambers of the burners, for safety reasons, such burners mix the combustion air with the fuel (typically natural gas) in the combustion chambers and do not produce the hotter more uniform flame patterns of burners which use premixed air/fuel supply systems. Thus, the method and burner/air ring assembly of the present invention, enable the use of air cooled burners with premixed air/fuel supply systems for a hotter, more uniform flame pattern without the need for a second air supply to cool the burner.